Narrative:

Aircraft was enroute when we diverted after we declared an emergency. At FL370 the first officer side attitude indicator displayed 10 degrees nose up; then held a few minutes at which point it started slowly climbing to 12 to 15 degrees. At this point the indication started climbing rapidly then started fluctuating up and down and the autopilot disengaged; the aircraft was physically level up to this stage. After the autopilot disengaged the ahrs 2 fail message appeared and per the QRH we selected the #1 ahrs data to the #2 side. At this point the #2 yaw damper disengaged and the YD2 fault status message appeared and the stabilizer trim and mach trim caution messages and the rudder limiter fault and pitch feel fault status messages appeared. The rudder began to yaw to the lt and rt uncommanded. We re-engaged the stabilizer trim; mach trim and #2 yaw damper and the messages cleared. Shortly afterward the #2 yaw damper disengaged again and the yd 2 fault status message reappeared and was the only message reappearing once below FL240. At FL370 the rudder felt heavier but was attributed to the higher airspeed at the time. We continued to correct for the uncommanded rudder movement all the way to the field and elected to land with the flaps at 20 degrees to maintain better rudder control without additional issues. Due to flaps 20 and little flare we landed hard. We were concentrating on the flight controls and did not attempt to slow the descent for a lower vertical speed due to our focus on controlling the rudder during the landing. We pulled the fdr and cvr breakers; and contacted dispatch and maintenance control to write everything up. [Landing flaps 20 in these conditions] was not outlined in the QRH. However; given all the available information I had at hand; I elected to land non-SOP. Focus during the landing was given on getting the aircraft on the ground and not flare; resulting in a hard landing. This would be an excellent aqp scenario!

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Original NASA ASRS Text

Title: A CRJ900 #2 AHRS failed followed by a yaw damper fault; uncommanded rudder movement; STAB and MACH TRIM cautions; RUDDER LIMITER and PITCH FEEL faults. An emergency was declared and the flight diverted to an enroute airport. Reporter stated simulator training with yaw dampers off would be valuable in dealing with this problem.

Narrative: Aircraft was enroute when we diverted after we declared an emergency. At FL370 the First Officer side attitude indicator displayed 10 degrees nose up; then held a few minutes at which point it started slowly climbing to 12 to 15 degrees. At this point the indication started climbing rapidly then started fluctuating up and down and the autopilot disengaged; the aircraft was physically level up to this stage. After the autopilot disengaged the AHRS 2 FAIL message appeared and per the QRH we selected the #1 AHRS data to the #2 side. At this point the #2 yaw damper disengaged and the YD2 FAULT status message appeared and the STAB TRIM and MACH TRIM caution messages and the RUDDER LIMITER FAULT and PITCH FEEL FAULT status messages appeared. The rudder began to yaw to the LT and RT uncommanded. We re-engaged the STAB trim; MACH trim and #2 yaw damper and the messages cleared. Shortly afterward the #2 yaw damper disengaged again and the YD 2 FAULT status message reappeared and was the only message reappearing once below FL240. At FL370 the rudder felt heavier but was attributed to the higher airspeed at the time. We continued to correct for the uncommanded rudder movement all the way to the field and elected to land with the flaps at 20 degrees to maintain better rudder control without additional issues. Due to flaps 20 and little flare we landed hard. We were concentrating on the flight controls and did not attempt to slow the descent for a lower vertical speed due to our focus on controlling the rudder during the landing. We pulled the FDR and CVR breakers; and contacted Dispatch and Maintenance Control to write everything up. [Landing flaps 20 in these conditions] was not outlined in the QRH. However; given all the available information I had at hand; I elected to land non-SOP. Focus during the landing was given on getting the aircraft on the ground and not flare; resulting in a hard landing. This would be an excellent AQP scenario!

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.